1. Field of the Invention
The present invention relates to a process for the production of alkyl formates from the reaction of a carbon monoxide containing gas and an alkyl alcohol and, more particularly, to an improved process for the production of methyl formate from the reaction of carbon monoxide and methanol in the presence of high concentrations of a homogeneous alkali metal methoxide catalyst at elevated pressures and relatively high temperatures.
Carbon monoxide is a common constituent of fuel gases, including synthesis gas (syngas), water gas, steamhydrocarbon reforming gases, blast furnace gas and the like. Removing and recovering the carbon monoxide content from these fuel gases, either as a step in purifying the fuel gas or for providing a source of carbon monoxide as a raw material, is well known in the art.
2. Description of the Prior Art
The industrial production of the alkyl formates, particularly methyl formate, has encountered a number of difficulties which have frustrated the development of a successful process. For example, the reaction synthesizing methyl formate from CO and methanol is quite exothermic, thereby creating substantial heat removal problems. Additionally, the traditional catalysts of choice, i.e., the alkali metal methoxides, have a substantial solubility in the alkyl alcohols, e.g., methanol, but a very low solubility in the desired alkyl formate, e.g., methyl formate, products of the reaction; consequently, a solid catalyst precipitate may form during the process and create substantial process impediments, e.g., clogging the pipes of the apparatus and frustrating effective heat transfer therein. Also, when using the low catalyst concentrations of the prior art, the reaction will be slow and require long residence times, and thus substantial equipment costs.
U.S. Pat. No. 3,716,619 discloses a process for recovering CO from blast furnace gas by compressing the gas and then reacting CO with a lower alcohol to form an alkyl formate. The formate is separated from the fuel gas and the CO is regenerated by decomposition of the formate. Such a process requires a low concentration of sodium methoxide as catalyst, and the liquid phase reaction is carried out at relatively modest temperatures, thereby frustrating an economical operation.
U.S. Pat. No. 4,216,336 discloses a process for the production of methyl formate whereby a gas containing CO is reacted at 70.degree. to 110.degree. C. and 20 to 110 bars in a reaction zone with a liquid mixture containing methanol and a catalyst. The process is further characterized by the recycle liquid reaction mixture being sucked in and dispersed in a certain mechanical manner in the current of gas introduced into the reaction zone. The amounts of sodium methoxide catalyst suitable for the process and the resulting reaction rates, however, are still relatively minimal.
German Patent Specification No. 926,785 also utilizes a small amount of catalyst so as to prevent precipitation thereof, but the resulting yields are uneconomic and the process also requires mechanical stirring at the extremely high pressures involved.
German Patent Specification No. 1,046,602 utilizes a two stage reaction zone for the contacting of carbon monoxide with methanol. However, the process requires that the CO pressure, the temperature of the cooling water, the reactant purity and other parameters be constantly monitored.
German Patent Specification No. 1,147,214 also contacts CO with methanol, but is an extremely cumbersome process.
Applicants have discovered a novel, improved process of synthesizing alkyl formates, particularly methyl formate, in a liquid phase reaction involving contacting an alkyl alcohol, e.g., methanol, with a CO containing gas, e.g., syngas, present at relatively high partial pressures in the presence of a homogeneous alkali metal methoxide, e.g., sodium methoxide, catalyst. The synthesis is conducted in, preferably, a two stage reaction zone in a low conversion process in which the CO containing gas is contacted in each zone with a fresh recycled alcohol stream containing high catalyst concentrations, under reaction zone conditions favoring high reaction rates, e.g., a high temperature reaction zone.
Accordingly, it is an object of the present invention to provide an improved process for the production of alkyl formates, particularly methyl formate, from a CO containing pressurized gas, e.g., a coal or heavy residual oil syngas, involving minimal capital expense, high catalyst concentrations and reaction rates and minimal heat requirements.
It is another object of the invention to provide an industrially acceptable process involving low per pass conversions of an alkyl alcohol into the corresponding alkyl formate.
It is still another object of this invention to develop a process having excellent conversions of carbon monoxide into methyl formate.